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| Repower Articles |
| Building "Miss Rebecca" - A 26' Jack Tar, Designed by Arch Davis |
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| After six years of effort, construction was completed and the boat launched
in the spring of 2000. I found the most nerve-wracking time of a boat building
project is the launch and subsequent shakedown. I soon found I had little
to be concerned about. Based on the boat's weight and horsepower, the propeller
calculations specified a top speed of 23+ knots. On her first run we reached
23.5 - right on the money. |
| The lobster boat design was everything I'd hoped. She's fast, roomy, incredibly
stable, and economical to operate. On the first shakedown run of 70 miles,
averaging 20 knots, fuel economy was 2.5 mpg. Subsequent runs at a comfortable
cruising speed of 17 knots resulted in fuel economy passing 3 mpg. |
| Some Final Thoughts |
| My success with this project can be attributed to many factors, including
Tony’s interest in my project. One final note after berthing "Miss
Rebecca" at the commercial fishing docks in Oceanside Harbor, my new
neighbors stopped by for a visit. Soon we were talking about all aspects
of boats, including my shiny Cummins engine. It came as no surprise when
three of them knew of Tony's work. One comment sounded familiar too; "He
really knows his stuff, he's going to do my new exhaust."Seems good
news travels fast on the docks. |
| Trial Results and Post Trial Follow-up |
| Based on my performance tests I believe I am over pitched by 1". Although
I can reach full RPM, the boat has a hard time staying at full RPM. RPM
falls off in turns and fluctuates between 2500 and 2600 RPM. Later this
fall I will pull the prop and have it repitched to 20x21. |
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| Transmission: |
ZF Marine ZF 63A
(ZF Hurth HSW630A)
Ratio: 1.5:1 |
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| Propeller: |
4 Blade
20" x 22"
RH |
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| RPM |
KNOTS |
GPH |
| 1200 |
7.7 |
1.5 |
| 1800 |
12.4 |
3.9 |
| 2000 |
14.5 |
5.3 |
| 2100 (cruise) |
15.7 |
6.2 |
| 2200 |
16.9 |
7.0 |
| 2400 |
19.7 |
9.0 |
| 2600 |
22.2 |
11.2 |
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| I've also found that I have insufficient air circulation within the engine
box after slowing down from cruise (16 k) to trolling speed (4 k). The air
temperature rise within the engine box exceeds the 30 degrees F. recommended
by Cummins. I've installed two blowers, one in and one out, connected to
a temperature switch that closes at 110 degrees. This has corrected that
problem. |
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Miss
Rebecca - 26' Jack Tar Designed by Arch Davis |
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